Semiconductor manufacturing system emits harmful waste gases such as a deposition gas containing SiH4 and a halogen-base gas (CHF3, C2F6, CF4, etc.), which should not be discharged directly into the atmosphere. It is therefore the general practice in the art to introduce such harmful waste gases into an abatement system where the waste gas is detoxified by way of combustion. According to the general waste gas treatment system, an auxiliary combustible gas is used to produce flames in a furnace for thereby combusting the waste gases.
In the combustion-type waste gas treatment system, the auxiliary combustible gas is usually in the form of a combination of a fuel gas such as hydrogen, a town gas, LPG, etc. and an oxidizing agent such as oxygen or air. Most of the operating cost of the combustion-type waste gas treatment system constitutes expenses required by the consumption of the fuel gas and the oxidizing agent. One of the indicators of the performance of combustion-type waste gas treatment system is how much harmful waste gases can be destroyed with a high efficiency with a small amount of auxiliary combustible gas. It is known in the art that when the deposition gas containing SiH4 is thermally destroyed, a powder of SiO2 is generated which tends to be deposited in the combustion chamber and cause various troubles to the combustion chamber. Consequently, a design approach to make the combustion chamber resistant to the deposition therein of a powder of SiO2 is also an important element in evaluating the combustion-type waste gas treatment system.
One general burner for use in conventional combustion-type waste gas treatment system is shown in FIGS. 28 and 29 of the accompanying drawings. As shown in FIGS. 28 and 29, the burner has a waste gas nozzle 2 defined centrally in the ceiling of a cylindrical combustion chamber 1, for introducing a waste gas A to be treated into the combustion chamber 1, and a plurality of auxiliary combustible gas nozzles 3 defined in the ceiling of the cylindrical combustion chamber 1 around the waste gas nozzle 2, for introducing an auxiliary combustible gas B into the combustion chamber 1, with a combustion gas outlet 4 integrally joined to the lower end of the combustion chamber 1. The auxiliary combustible gas B ejected from the auxiliary combustible gas nozzles 3 produces flames in a circular pattern. While the waste gas A passes centrally through the circular pattern of flames, the waste gas A is mixed with and combusted by the flames, emitting a combustion exhaust gas which is discharged out of the combustion chamber 1 through the combustion gas outlet 4.
With the conventional burner, however, since the flames produced by the auxiliary combustible gas are formed in front of the auxiliary combustible gas nozzles, the waste gas discharged forward from the waste gas nozzle which is positioned inwardly of the auxiliary combustible gas nozzles is not necessarily sufficiently mixed with the flames, and hence the efficiency of destruction of the waste gas is not sufficiently high. In order to increase the efficiency of destruction, it is necessary to increase the amount of auxiliary combustible gas to produce large flames, which allow the waste gas to be easily combusted and destroyed. However, the amount of auxiliary combustible gas, which does not contribute to the destruction of the waste gas is also increased, resulting in an increase in the operating cost of the combustion-type waste gas treatment system.
When a SiH4 gas is destroyed by way of oxidization, a produced powder of SiO2 is attached to and deposited on wall surfaces where the exhaust gas flows slowly. If the concentration of SiH4 in the waste gas is high, then the powder of SiO2 is produced and deposited in an increased quantity on the wall surfaces. In worst cases, an auxiliary combustible gas may not be continuously combusted, and it may be necessary to shut off the combustion-type waste gas treatment system for removal of the deposited powder.